Mediterranean-type ecosystems are fire-prone environments where species have evolved in the presence of seasonal summer conditions and frequent fires. In these environments, many species have seeds with impermeable hard coats that impose physical seed dormancy which prevents seed germination until it is broken by any factor such as fire or high summer temperatures. Most studies have usually focused on the isolated effects of fire or summer temperatures on the release of physical seed dormancy. However, both factors frequently operate together because when a fire occurs, usually in summer, seeds in the soil suffer not only the heat shock during the fire, but also the high summer temperatures. Nevertheless, the combined effect of both factors is almost unknown. In this investigation, we studied the isolated and combined effects of heat shock and the high temperatures of summer. The main objective was to evaluate whether the timing in which seeds are exposed to a heat shock during the period of high summer temperatures affects seed germination. We exposed the seeds of 12 Cistaceae species to three different treatments, in which heat shock (100 °C for 10 min) was applied before, after, or before + after they were exposed to summer temperatures (50/20 °C for 1 month). Although fire was the main factor breaking physical dormancy, its effects were regulated by the timing when it was simulated. We found that summer temperatures following heat shock had negative effects on seed germination since a high proportion of seeds remained dormant. On the contrary, when summer temperatures preceded heat shock, physical dormancy was broken, and germination increased. Timing of fire during summer plays an important role in controlling seed germination of Cistaceae. Our results provide a novel explanation for the higher Cistaceae seedling emergence found in the field after late season fires. Additionally, we can carefully draw conclusions for fire management since prescribed burnings would have different effects depending on when they were carried out.

中文翻译：

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夏季的火灾时间决定了地中海苍耳科植物种子的发芽

地中海型生态系统是易发生火灾的环境，物种是在季节性夏季条件和频繁火灾的情况下进化的。在这些环境中，许多物种的种子具有不透水的硬皮，这会导致种子物理休眠，从而阻止种子发芽，直到被火灾或夏季高温等任何因素破坏为止。大多数研究通常集中于火灾或夏季温度对种子物理休眠释放的孤立影响。然而，这两个因素经常一起作用，因为当火灾发生时，通常是在夏季，土壤中的种子不仅会受到火灾期间的热冲击，还会受到夏季高温的影响。然而，这两个因素的综合影响几乎是未知的。在本次调查中，我们研究了热休克和夏季高温的单独影响和综合影响。主要目的是评估夏季高温期间种子暴露于热休克的时间是否会影响种子发芽。我们将 12 种肉苁科物种的种子暴露于三种不同的处理中，其中在暴露于夏季温度（50/20°C，1 个月）之前、之后或之前+之后应用热休克（100°C，10 分钟）。 ）。虽然火是打破物理休眠的主要因素，但其效果却受到模拟时间的调节。我们发现热激后的夏季气温对种子发芽有负面影响，因为很大一部分种子处于休眠状态。相反，当夏季温度高于热休克时，身体休眠被打破，且发芽率增加。夏季用火的时间对于控制肉苁科种子的发芽起着重要作用。我们的研究结果为晚季火灾后田间发现的肉苁科幼苗出苗率较高提供了新颖的解释。此外，我们可以仔细地得出火灾管理的结论，因为规定的燃烧根据其进行的时间会产生不同的效果。